What is boundary value analysis and equivalence partitioning?
- boundary value analysis
- equivalence partitioning
- test design
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Model answer
Equivalence partitioning divides inputs into groups that should behave the same way, test one value from each group instead of every possible input. Example: age field accepts 18-65 → partitions: <18 (invalid), 18-65 (valid), >65 (invalid). Boundary value analysis tests at the edges of partitions: 17, 18, 65, 66. Bugs cluster at boundaries because code uses <, <=, >, >= and off-by-one errors are common. Together, these techniques reduce test cases while maximizing defect detection.
What interviewers listen for
- Risk-based prioritisationYou can defend skipping coverage on a path because the risk maths supports it.
- Test design fluencyYou apply equivalence partitioning and decision tables to concrete inputs in real time.
- Metric judgmentYou distinguish between metrics that drive learning and metrics that drive theatre.
- Strategy under constraintYou can produce a defensible plan when the team has half the time and twice the scope.